The proposed research will investigate the extent, direction, and origin of survey mode effects in epidemiological studies of alcohol and drug use. Very little is known about the extent to which data quality and the validity of prevalence estimates differ by survey mode, for a topic as sensitive as illicit drug use. The major research objective will be to isolate specific survey design features that affect the outcome of drug surveys, including: (1) method of interview administration (telephone versus personal, interviewer-administered versus self-administered drug items); and (2) sample coverage bias due to the exclusion of non-telephone households in random digit dial (RDD) samples. Nonresponse bias, time of measurement, questionnaire wording, and method of screening will be controlled. Analyses will examine: (1) the impact of self-administered answer sheets on levels of drug use reported in personal interviews; (2) the impact of the means of communication itself (telephone versus face-to -face) on response tendencies, when mode effects due to sample coverage and nonresponse are controlled; (3) how the influence of survey mode on self- reported drug use differs by respondents' race/ethnicity, age, or sex; (4) the influence of survey mode on respondents' rapport, cooperativeness, comprehension, and interview mode preference; and (5) the extent to which population estimates of drug use differ when nontelephone households are excluded from the sample. Two surveys of the State of New Jersey will be conducted. In survey 1, respondents selected through a multistage area probability sample of the state will be randomly assigned to a telephone, personal, or self- administered interview. Survey 2 will be an RDD telephone survey of the state. Eligible respondents will be adolescents and young adults (ages 12-34), the population segments with the highest rates of illicit drug use. Blacks and Hispanics will oversampled. Drug categories will include tobacco, alcohol, marijuana, cocaine, inhalants, and the nonmedical use of prescription drugs.